Disc drive memory systems store digital information that is recorded on concentric tracks on a magnetic disc medium. At least one disc is rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is typically used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the stator. One type of motor has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the sleeve, while maintaining alignment of the spindle to the shaft.
Disc drive memory systems are being utilized in progressively more environments besides traditional stationary computing environments. Recently, these memory systems are incorporated into devices that are operated in mobile environments including digital cameras, digital video cameras, video game consoles and personal music players, in addition to portable computers. These mobile devices are frequently subjected to various magnitudes of mechanical shock as a result of handling. As such, performance and design needs have intensified including improved resistance to shock events including axial and angular shock resistance, vibration response, and improved robustness.
The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information. Moreover, a demand exists for increased storage capacity and smaller disc drives, which has led to the design of higher recording areal density such that the read/write heads are placed increasingly closer to the disc surface. Precise alignment of the heads with the storage tracks is needed to allow discs to be designed with greater track densities, thereby allowing smaller discs and/or increasing the storage capacity of the discs. Because rotational accuracy is critical, many disc drives presently utilize a spindle motor having a fluid dynamic bearing (FDB) situated between a shaft and sleeve to support a hub and the disc for rotation. The stiffness of the fluid dynamic bearing is critical so that the rotating load is accurately and stably supported on the spindle without wobble or tilt. In a hydrodynamic bearing, a lubricating fluid is provided between a fixed member bearing surface and a rotating member bearing surface of the disc drive. Hydrodynamic bearings, however, suffer from sensitivity to external loads or mechanical shock.
A method of providing a compact fluid sealing system is to employ asymmetric sealing. Many bearings utilize an asymmetric fluid sealing system with a capillary seal situated on one end of the bearing, and a grooved pumping seal on an opposite bearing end. However, in these sealing systems, a problem arises known as jog, jog being the rapid and repeated opening and closing of axial spaces between relatively rotatable components that can dispel oil from, or draw air into, these spaces. In contemporary designs, unless the flow resistance of a recirculation channel is sufficiently low, oil will either be expelled from the fluid seals during compression, or air will be drawn into the fluid seals during expansion.
Further, a sufficient amount of lubricant such as oil must be maintained in a capillary seal reservoir to offset losses. If a shock event occurs with a motor having an insufficient volume of lubricant, rotating surfaces may come in direct contact with stationary components. The dry surface-to-surface contact may lead to particle generation or galling and lock-up of the motor during contact. Particle generation and contamination of the bearing fluid may also result in reduced performance or failure of the spindle motor or disc drive components.